A medium size city such as Quebec City, QC, Canada has four (4) water treatment plants connected to 2300 km of drinking water conduits and two (2) waste water treatment plants connected to 3000 km of sewer conduits to serve a population of about half a million people. Water systems of larger cities are comparatively larger and form very complex networks.
Maintenance operations are frequently required in these water systems. Such operations oftentimes require the closing of underground water valves to prevent flooding of conduits, allowing access by maintenance personnel. Accidental or malicious operation of an underground water valve while a worker is present in a conduit can have dramatic implications: a conduit deep underground may be filled in just a few seconds by opening a 12-inch water main. In a large city having hundreds of underground water valves spread over a large network of streets and underground conduits, such accidents are possible and must be prevented.
FIG. 1 (Prior Art) shows a worker manipulating an underground valve before accessing a manhole. On a street 10, a worker 12 has removed a cap 14 to get access to a vertical conduit 16 at the bottom of which a underground water valve (not shown) controls the flow of water in an underground conduit (not shown). The worker 12 uses an elongated tool 18 to close the underground water valve. The underground water valve may be quite deep underneath the surface of the street 10, generally at least below the frost line, for example at a depth between 12 and 15 feet. Before accessing the underground conduit via a manhole 20, the worker 12 would traditionally replace the cap 14 to close the vertical conduit 16, preventing access to the underground water valve. The worker 12 would use spray paint from a can 22 to mark the cap 14, indicating to other workers (not shown) that the underground water valve is closed and should remain closed for safety reasons.
Conventionally, no technical means other than a mere visual indication was available to prevent accidental or malicious operation of the underground water valve. Opening the underground water valve when the worker 12 was present in the underground conduit could have fatal consequence.
A conduit blocking device has been implemented and tested and provides some improvements to worker safety. FIG. 2a (Prior Art) is a perspective view of a conventional conduit blocking device. FIG. 2b (Prior Art) shows the effect of applying compression on the conventional conduit blocking device of FIG. 2a. FIG. 3a (Prior Art) shows a first installation phase of the conventional conduit blocking device of FIG. 2a. FIG. 3b (Prior Art) shows a second installation phase of the conventional conduit blocking device of FIG. 2a. FIG. 4 (Prior Art) shows a padlock mounted to the conventional conduit blocking device of FIG. 2a. Referring at once to FIGS. 2a, 2b, 3a, 3b and 4, a conduit blocking device 30 comprises a top plate 32 and a bottom plate (not shown) adapted to compress a donut-shaped polymer ring 34. A bolt 36 is fixedly mounted to the bottom plate and passes through an opening (not shown) at the center of the top plate 32. A nut 38 is mounted to the bolt 36 and is rotated to apply or release pressure on top plate 32 and on the ring 34. The bolt 36 has an aperture 40 at its top. A wire 42 is attached to the bottom plate and passes through openings 44 of the top plate 32, through openings (not shown) within the ring 34 and reaches the bottom plate. The wire 42 forms a loop at its top (not shown). As shown specifically on FIG. 2b, using a tool 46 to rotate the nut 38 causes a pressure to be applied between the top plate 38 and the bottom plate, whereby a height 48 of the ring 34 is reduced while a width 50 of the ring 34 expands.
Referring specifically to FIGS. 3a and 3b, in operation, after having closed the underground water valve, the worker 12 holds the conduit blocking device 30 by its wire 42 and lowers the conduit blocking device 30 partway within the vertical conduit 16 (FIG. 3a). The worker 12 uses the tool 46 to rotate the nut 38 (FIG. 3b), causing the ring 34 to compress. The width 50 of the ring 34 expands until it mates with the interior surface 54 of the vertical conduit 16. Under this condition, the conduit blocking device 30 is locked in position within the vertical conduit 16, blocking access to the underground water valve located at the bottom of the vertical conduit 16. As shown specifically on FIG. 4, a padlock 52 is mounted to the aperture 40 on the top of the bolt 36. Accidental or malicious operation of the underground water valve is prevented.
Although the conduit blocking device 30 provides significant safety improvements over the conventional techniques, it still suffers from several inconveniences. One such inconvenience lies in the fact that at least some of the components of the conduit blocking device 30, for example the bottom plate, may fall within the vertical conduit 16, down to a level of the underground water valve. This incident may easily occur because the worker 12 cannot see the position of the nut 38 in relation to the top of the bolt 36 when rotating the nut 38 to release the pressure on the top plate 32 and on the ring 34. Because the diameter of the bottom plate is only slightly inferior to the interior diameter of the vertical conduit 16 and because of the depth at which the underground water valve is located at the bottom of the vertical conduit 16, removing the bottom plate or any other part of the conduit blocking device 30 can be quite difficult and time consuming; possibly requiring digging the street 10 down to the bottom of the vertical conduit 16.
Another inconvenience of the conduit blocking device 30 is that it may retain water that may enter the top of the vertical conduit 16. Operation of the conduit blocking device 30 in winter conditions may be quite difficult as water may freeze at a level where the padlock 52, the bolt 36 and the nut 38 are located, expansion of the water as it freezes possibly causing a failure of the upper part of the vertical conduit 16. At least because water conduit failures are fairly frequent in the winter, this situation is expected to be frequent as well.
Therefore, there is a need for improvements that compensate for operational problems of conduit blocking devices used to overcome safety concerns of workers accessing underground conduits.